1. Field of the invention
The invention proceeds from a process for reducing eddy currents in a superconductor strip the preamble of patent claim 1, and from a superconductor arrangement according to the preamble of patent claim 2.
2. Discussion of background
In the respective preamble, the invention relates to a prior art as it is known from DE-C2-2,654,924. In order to overcome the disadvantage of brittleness with respect to mechanical stresses, a strip-like conductor or compound wire, around which a superconducting layer of Nb.sub.3 Sn around strip of Nb is arranged, has been proposed. A stabilizing layer of copper or of a copper alloy is arranged around the superconducting layer, a layer, usually soldered, being arranged between the superconducting layer and the stabilizing layer. An outermost insulating layer is arranged around the stabilizing layer. It is given as disadvantageous that the strip has an instability in the form of a flux jump due to a non-uniform magnetic field, which is caused by geometrical anisotropy and leads to problems in the development of a magnet. Furthermore, it is known to wind individual compound cables around a rectangular or round tube of a stabilizing and/or a reinforcing material. In order, in the case of alternating current applications, to avoid disadvantageous effects due to a coupling current, the superconducting cores or strands are twisted together. A coupling current can also be reduced by providing a different conductivity for the respective cores. Furthermore, an increased contact resistance between the relevant cores can avoid a loop of the coupling current in an effective way. In order to avoid eddy-current losses, it is provided that a stabilizing metal, such as copper, is used in an insulated and mutually separated state, instead of in a continuous, solid form. It can also be provided that the copper is subdivided by a material of high electrical resistance into individual sections.
The disadvantage of this is the relatively expensive production of compound cables.
Concerning the relevant state of the art, reference may further be made to a publication by T. R. Dinger et al., Direct Observation of Electronic Anisotropy in Single-Crystal Y.sub.1 Ba.sub.2 Cu.sub.3 O.sub.7-x, in the Americal journal: Physical Review Letters, Vol. 58, Nr. 25, 22.6.1987, pages 2687-2690. There is a description in that reference of the electrical behavior of anisotropic high-temperature oxide superconductors, which have a smaller critical current density in a specific direction than in all other directions.
Production of orientated films of high-temperature superconductors is known from a publication by S.Jin et al., High critical currents in Y-Ba-Cu-O superconductors, in the American journal: Appl. Phys. Lett. 52. (24), 13.6.1988, pages 2074 to 2076.